Spinning of high molecular weight polyamide filaments



1967 R. G. GOSDEN 3,346,684

SPINNING OF HIGH MOLECULAR WEIGHT POLYAMIDE FILAMENTS v Filed May 7, 1964 I Attorneys United States Patent 3,346,684 SPINNING OF HIGH MOLECULAR WEIGHT POLYAMIDE FILAMENTS Raymond George Gosden, Cwmbran, England, assignor to British Nylon Spinners Limited, Pontypool, England Filed May 7, 1964, Ser. No. 365,665

Claims priority, application Great Britain, May 25, 1963,

20,970/ 63 2 Claims. (Cl. 264-476) This invention relates to the spinning of high molecular weight polyamide filaments, and more particularly to those processes of melt spinning wherein the filaments, after solidification, are treated with steam before being wound up.

In the melt spinning of filaments, the latter on first emerging from the spinneret orifices are in a soft and tacky condition. Such filaments would stick to a thread guide. As the extruded material gets further and further from the spinneret, it gradually solidifies. In other words, the filaments solidify as they cool. In any case the point of solidification is to be understood as the point where the extruded filament ceasesto be tacky. In vertical spinning (and melt-spinning is usually carried out vertically downwards) the solidification point will thus be the highest point at which any thread guide may be placed.

In the case of melt-spun synthetic linear polyamides of high molecular weight, e.g. polyhexamethylene adipamide, the extruded filaments are treated with steam mainly in order that they may acquire a water content and that the resulting yarn may suffer little or no further dimensional change on storage in the factory atmosphere, which may possess a relative humidity of, for example 65%. For this purpose the extruded filaments are usually for the sake of convenience gathered together in a thread guide, known as the convergence guide, and the bundle of filaments thus obtained is passed downwards through a tube in which an atmosphere of steam is maintained. The convergence guide is normally placed at the top of the steam tube and close to the point at which the filaments first solidify.

After any other desirable treatment such as the application of a finish or size, the extruded filaments are wound up by conventional means which in effect pull the extruded filaments from the spinneret.

The polyamide filaments, e.g. polyhexamethylene adipamide filaments are then submitted to a subsequent drawing operation in the solid state whichintroduces orientation into the polyamide molecules constituting the filaments and develops a high tenacity and other desirable textile properties therein. In the drawing operation the filaments may be elongated in the solid state to, say, 4-5 times their original length.

Now a melt spinning apparatus constitutes a large, elaborate and costly piece of plant. In other words such an apparatus involves considerable expense in the way of invested capital charges. For this reason polyamide filaments are commonly melt-spun at high speeds amounting to several thousand feet per minute It will thus be clear that a method of increasing the rateof output of such an apparatus could, other things being equal, be applied to effect important financial economies.

It is well-known that in 'a commercial melt-spinning process, the filaments being wound up at say 1000 metres perminute, most of the draw-down, perhaps 85% of the total draw-down occurs in the upper part of the column of meltspun filaments Where the latter have not yet solidified. This part of the draw-down is responsible for some orientation in the molecules of which the filaments are composed. The remaining part of the draw-down (15%) takes place after solidification of the filaments and produces further orientation of the molecules. (For the purpose of clarity it may be stated that the draw-down-during melt-spin- Patented Oct. 10, 1967 ning is defined as the diameter of the spinneret orifice divided by the diameter of the wound up filament.) The polyamide molecules are further oriented when the filaments are subsequently drawn in the solid state on a drawing machine in order to develop their tenacity, a process already alluded to above. As noted, the convergence guide is placed close to the point of solidification of the filaments (before they are treated with steam) and therefore the degree of orientation possessed by the melt-spun filaments (before the subsequent drawing step on the drawing machine) is due to :and thus depends on, inter alia, the degree of drawn-down (i.e. drawing or elongation) which takes place after the filaments have passed the convergence guide, i.e. below the convergence guide. This elongation may amount to about 30% for example. A measure of the degree of orientation is provided by a determination of the birefringence of the filaments. A further increase in degree of orientation (and accordingly birefringence) is effected during the subsequent drawing on the drawing machine. The finished filaments thus exhibit a higher birefringence than the melt-spun filaments.

In the course of manufacture of polyamide filaments by melt-spinning and drawing it will be understood that'in order that the product, i.e. finished filaments, may have uniform properties along their length, great attention must be paid to maintaining all the conditions of the process as far as possible at constant values. In other words the permissible variation is very small if the quality of the product is to be maintained at a high level. In this connection it must be remembered that the properties of the filaments which are of commercial importance are numerous being both physical and chemical e.g. tenacity, elasticity, extensibility, birefringence, flexibility, moisture aflinity, shrinkage when wetted, thermal properties, light stability, dyeing properties. The process conditions include temperature of melt-pool, rate of extrusion of polyamide in kgm./hour, linear rate of winding up, rate of cooling of the extruded filaments (which influences the spherulitic structure of the polyamides, namely the number and size of the spherulites produced), degree of draw down, humidity of the surrounding atmosphere. The linear rate of winding up or linear speed of the winding up means in the linear rate or speed at which the filaments are wound up. The denier of the finished, i.e. drawn yarn is equal to the denier of the melt-spun yarn divided by the effective draw ratio, the denier of the melt-spun yarn being proportional to the rate of extrusion of the polyamide (i.e. rate of output of polyamide by weight) and inversely proportional to the rate of winding up. It will be evident that for a given rate of winding up, the rate of output is proportional to the denier of the melt spun yarn. In practice numerous melt-spinning processes are operated to provide yarns of different deniers and having various numbers of filaments but in every case the conditions need careful adjustment.

Extensive investigation has now shown that it is possible to increase the rate of output of a melt-spinning machine by changing the process in the following manner.

Let a melt-spinning process be considered wherein x kgm. of polyamide are extruded per hour, the denier of the wound upyarn is y and the latter is subsequently drawn at a draw ratio of 4 in a drawing machine. The denier of the drawn yarn will accordingly be A y.

Suppose now that the rate of extrusion is increased by, say, 10% to 1.1x kgm. of polyamide per hour. The denier of the wound-up filaments will therefore be 10% greater. If, however, the draw ratio in the subsequent drawing operation be increased from 4 to 4.4 i.e. by 10%, the final denier of the drawn yarn will remain at its original value i.e. A y. But the drawn yarn Will not be satisfactory because the increased drawn ratio will have undesirably increased the degree of orientation and decreased the extensibility at break. It has now been found that by increasing, e.g. with forwarding means consisting of driven nip rolls mounted just below the convergence guide, the linear speed at which the filaments pass the guide so that this speed is nearly equal to (i.e. within a few percent of) the speed of winding up, the elongation of the filaments occurring below the convergence guide can be substantially eliminated, with consequential reduction in the orientation possessed by the melt-spun filaments. For example their birefringence (which is a measure of orientation) may be reduced from 0.020 to 0.015. In this manner it is possible to correct the undesirable effect of the increased drawn ratio alluded to above so that satisfactory yarn is produced at the higher rate of output.

The change in the process could be described as the transfer of some drawng i.e. introduction of orientation into the molecules of the filaments, from the melt-spinning operation to the subsequent drawing operation. Now the surprising discovery has been made that this change in the process can be efiected without noticeably or seriously prejudicing the properties of the yarn, as would have been feared for the reasons explained above.

Accordingly the invention consists of a process of melt-spinning high molecular weight synthetic linear polyamides into filaments wherein the latter after solidification are treated with steam and wound up by conventional means characterised in that the filaments after solidification are forwarded by conventional forwarding means at a controlled linear rate which is equal to or nearly equal to the linear speed of winding up, i.e. differing by not more than a few percent therefrom, e.g. /2 1%, 2% or 3 The controlled linear speed of the forwarding means is preferably slightly less than that of the winding up so as to hold the running filaments taut and steady.

The invention includes an apparatus for carrying out the above process comprising a melter With a spinneret and a pumping means, a convergence guide, a forwarding means, a steamer (often known as a steam conditioner, because the steam conditions the filaments), a conventional winding up means, and a mechanical means to control the ratio of the linear speeds of the said forwarding means and winding up means.

The synthetic linear polyamide (which designation is intended to include interpolyamides) may be, for example, those quoted with their melting points below:

C. Poly-epsilon-caprolactam 214 Polyhexamethylene adipamide 248 Polyhex-amethylene sebacamide 209 Poly-kappa-aminoundecanoic acid 187 Interpolyamide from hexamethylene diammonium adipate and epsilon-caprolactam in the ratio by weight of 80:20 220 Frequently the cooling of the extruded polyamide filaments is accelerated by a blast of air directed across their path. In any case the point of solidification (below which is positioned the convergence guide, if used, and the present controlled forwarding means) depends on the rate of draw down and on the specific polyamide chosen. Some polyamide melting points have thus been quoted above.

The controlled forwarding means may be, for instance, driven nip rolls (already referred to) or a driven godet round which the filaments are passed, conveniently after they have been gathered together into a bundle by a convergence guide. No such guide may however, be necessary, if for example, a row of parallel filaments are spun from a series of spinneret holes in a straight line. In order to prevent undue oscillation of the filaments in the steamer it is preferred, as indicated above, that they be held taut by controlling the speed of the forwarding means at a few percent below that of the winding up means. In other words a very small degree of drawing or elongation is permitted to take place below the forwarding means.

The steamer or steam treating means may be variously constructed. Usually it is a vertically positioned open ended vessel of circular cross-section, i.e. a pipe, in which an atmosphere of steam is maintained and through which the filaments are passed on their Way downward to the winding up means. In the case of a row of parallel filaments, a steamer of rectangular cross-section would be suitable, on the assumption that no convergence guide Was used to gather the filaments into a bundle.

The following example is intended to illustrate, not limit, the invention.

Example With reference to FIGURE 1 of the accompanying diagrammatic drawings 20 filaments of polyhexamethylene adipamide are melt-spun (in accordance with known art) by means of the melter 1, gathered together in the guide 2, passed downwards (without the nip rolls shown at 3) through the steamer 4, and wound up at a linear speed of 1200 metres per minute by conventional means to form a cake 5. The extruded filaments are cooled by a blast of air indicated by the arrow 6. The rate of output of polyamide from the melter 1 is 2.9 kgm. per hour. The total denier of the wound up filaments is 182. The latter are then drawn to 3 times their original length, as illustrated in FIGURE 2 of the accompanying drawings wherein 5 is the supply cake, 7 are the feed rolls, 8 the draw rolls and 9 a conventional winding up bobbin. The peripheral speed of the draw rolls 8 is slightly greater than three times that of the feed rolls 7 in order to allow for any slight slip of the filaments and their subsequent retraction. The resulting 20-filament yarn accordingly having a total denier of 60.

The above process is now changed in accordance with the present invention by introducing the nip rolls shown at 3 in FIGURE 1 of the drawings, which rolls are driven so that the filaments are forwarded at a few percent less than the winding up speed which is unchanged at 1200 metres per minute, namely at 1160 metres per minute. The ratio of linear forwarding speed to linear windup speed is controlled by a suitable mechanical means 10. At the same time the output of the melter 1 is increased by 10%, viz. to 3.2 kgm. per hour.

The total denier of the wound up filaments at 5 in FIGURE 1 is then found to be 10% greater i.e. 200. In other words the rate of output of the melter 1 has been increased by 10%. The wound up filaments are drawn at an increased effective draw ratio of 3.3 to compensate for their greater denier, so that the resulting drawn yarn still has a total denier of 60'. Despite the increased output of the melt spinning apparatus achieved by the invention, the properties of the drawn yarn are little changed, thus:

What I claim is:

1. In a process of making high molecular weight synthetic linear polyamides into filaments wherein the polyamides are melt-spun in the form of molten filaments and wherein the filaments are solidified, treated with steam, wound up and subsequently unwound and drawn, the improvement which increases the mass rate of melt spinning and drawing without adversely affecting the hirefringence and extensibility of the drawn filaments, said improvement comprising: increasing the mass rate of melt spinning the filaments thereby forming filaments of greater denier; positively forwarding the filaments, almost immediately after solidification and before treating with steam by contacting the filaments with a forwarding means, at a linear speed which is substantially equal to the linear speed of winding up whereby the denier of the Wound up filaments is increased and whereby the filaments rnay be drawn subsequently to a greater extent without producing undesirable properties in the drawn filaments.

2. A process as in claim 1 wherein the filaments are drawn to an extent such that the final denier is about the same as the denier produced by the initial overall process before increasing the rate of melt spinning whereby the output of the initial process is increased without any appreciable change in filament properties or denier.-

References Cited UNITED STATES PATENTS 2,273,105 2/1942 Heckert 188X 6 2,289,860 7/1942 Babcock 18-8 X 2,577,915 12/1951 Piller et al. 264-210 2,768,057 10/1956 Friederich 18--8 X 2,811,409 10/1957 Clapp et al 18-8 X 3,013,361 12/1961 McFadden 188 X 3,067,459 12/1962 Brand l88 X 3,070,839 1/1963 Thompson 188 X 3,216,187 11/1965 Chantry et a1 2 64--21O X FOREIGN PATENTS 556,640 4/1958 Canada. 661,999 11/1951 Great Britain.

ALEXANDER H. BRODMERKEL, Primary Examiner.

ROBERT F. WHITE, D. J. ARNOLD, Examiners.

J. H. WOO, Assistant Examiner. 

1. IN A PROCESS OF MAKING HIGH MOLECULAR WEIGHT SYNTHETIC LINEAR POLYAMIDES INTO FILAMENTS WHEREIN THE POLYAMIDES ARE MELT-SPUN IN THE FORM OF MOLTEN FILAMENTS AND WHEREIN THE FILAMENTS ARE SOLIDIFIED, TREATED WITH STEAM, WOUND UP AND SUBSEQUENTLY UNWOUND AND DRAWN, THE IMPROVEMENT WHICH INCREASES THE MASS RATE OF MELT SPINNING AND DRAWING WITHOUT ADVERSELY AFFECTING THE BIREFRINGENCE AND EXTENSIBILITY OF THE DRAWN FILAMENTS, SAID IMPROVEMENT COMPRISING: INCREASING THE MASS RATE OF MELT SPINNING THE FILAMENTS THEREBY FORMING FILAMENTS OF GREATER DENIER; POSITIVELY FORWARDING THE FILAMENTS, ALMOST IMMEDIATELY AFTER SOLIDIFICATION AND BEFORE TREATING WITH STEAM BY CONTACTING THE FILAMENTS WITH A FORWARDING MEANS, AT A LINEAR SPEED WHICH IS SUBSTANTIALLY EQUAL TO THE LINEAR SPEED OF WINDING UP WHEREBY THE DENIER OF THE WOUND UP FILAMENTS IS INCREASED AND WHEREBY THE FILAMENTS MAY BE DRAWN SUBSEQUENTLY TO A GREATER EXTENT WITHOUT PRODUCING UNDESIRABLE PROPERTIES IN THE DRAWN FILAMENTS. 